A major cost problem experienced by the electronics industry is the loss of solderability of electronic components, particularly during storage. Poor solderability of electronic component leads and printed wiring boards accounts for a large percentage of solder joint failures. Previous studies have determined that oxidation of the surface and underlying substrate and/or intermetallic layers of solderable components is a cause of this degradation. Solderability and the basic methods of sequential electrochemical reduction analysis and restoration of solderability are described in U.S. Pat. Nos. 5,262,022 and 5,104,494, the teachings of which are hereby incorporated by reference.
In the method of sequential electrochemical reduction analysis, surface oxides that interfere with the solderability of metals are detected by electrochemical reduction. The resulting data yields both the types and amounts of oxides present. For analysis of printed wiring board (PWB) through-holes and surface pads, an electrolytic solution is brought into contact with the area to be tested and electrical contact is made through another PWB feature that is electrically interconnected with the test area. Large component leads, such as resistor wires, can be evaluated conveniently by immersing the portion to be tested in the electrolyte solution and making electrical contact to a part of the lead above the level of the solution. However, testing of fine-pitched component leads is difficult because electrolyte solution tends to extend up the lead to the component body by capillary attraction. Because little or no unwetted area remains on the component lead, the cathode connecting lead generally comes into contact with the electrolyte solution. Thus, the cathode lead must have a high hydrogen overvoltage (i.e., the same as or higher than that of the tested component) and must be pre-reduced to avoid measurement errors from its reaction with the electrolyte. Also, the upper part of the component lead, where capillary attraction or "wicking" occurs, is usually not typical of the area to be soldered and can give misleading results when included as part of the analyzed area. Furthermore, penetration of electrolyte solution into non-hermetic seals between leads and the component body can result in damage to the device and grossly erroneous data from electrochemical analysis.
Another problem with many electrochemical analytical methods, including sequential electrochemical reduction analysis, is interference from oxygen that is present initially or is introduced through leaks in the electrolyte solution containment system. Electric current associated with electrochemical reduction of oxygen tends to mask the processes of interest and introduce errors into the analysis data. Thus, there is a need for an improved, quantitative, nondestructive method of analysis that is easily adapted for electrochemical testing of various electronic and corrosion resistant components.